Biomedical electrodes are used to either deliver to or receive electrical signals from those mammalian patients. The interface between the mammalian patient and the electrode is the outer layer of mammalian skin, called the stratum corneum. The natural protective nature of the stratum corneum provides an electrical barrier which is typically called skin impedance.
While there are no current maximum amounts of skin impedance recognized by the medical industry in a standard promulgated by the Association for the Advancement of Medicine (AAMI), skin impedance should be minimized to maximize the amount of faint electrical signals emanating from the body when the procedure involves diagnosis or monitoring of an organ of the body producing electrical signals. For example, the amount of skin impedance recognized by some members of the electrode industry for diagnostic medical electrodes ranges from about 1 to about 100 kohm and preferably from about 2 to about 15 kohm, whereas the amount of skin impedance for monitoring medical electrodes ranges from about 1 to about 100 kohm and preferably from about 5 to about 50 kohm. These impedances refer to the impedance of electrode monitoring device and skin together within the first 30 seconds of electrode application on the skin measured at a frequency of 10 Hz using a sinusoidal waveform of low intensity (&lt;10 .mu.A, peak-peak).
There are three principal means of reducing skin impedance: chemical, electrical and mechanical. A chemical means typically includes providing additional chloride ions (Cl.sup.-) between the skin and electrode to increase conductivity through the stratum corneum. An example of an electrical means is disclosed in PCT Patent Publication WO97/24060 (Carim et al.).
The traditional means of reducing skin impedance is mechanically removing a portion of the stratum corneum at the site of biomedical electrode placement on mammalian skin. One commercial skin abrader is a particulate-based strip of material sold by Minnesota Mining and Manufacturing Company of St. Paul, Minn., USA as 3M Skin Prep No. 2236 skin abrader, which instructs a user to tear a piece of material from a roll dispenser and to gently abrade, with moderate pressure, the skin where the electrode will be adhered. The strip is a laminate of mineral particulates on a flexible backing with a coating of adhesive on the opposing side, i.e., adhesive-backed sandpaper having about a 240 grit.
Another type of commercial skin abrader is associated with each individual biomedical electrode sold by Minnesota Mining and Manufacturing Company as 3M Red Dot No. 2249, 2255, 2259, 2260, 2270, 2271, 2274, and 9630 Monitoring Electrodes, where the sandpaper has a grit of about 600 and is a dot of material adhered to the protective release liner of the electrode.
The manufacture of biomedical electrodes is controlled by the various governmental health agencies responsible for assuring that safe and effective products reach the patient. One of the standards required by United States health agencies is called Good Manufacturing Practices (GMP), currently being replaced by Quality Systems Regulations (QSR).
The marketing of biomedical electrodes is subject to price and cost pressures of free enterprise competition among companies and the demands of customers responsible for patients such as health maintenance organizations (HMOs).
While sandpaper made by Minnesota Mining and Manufacturing Company is manufactured according to strict standards, sandpaper has a natural variability from particle to particle. Moreover, a product that relies on sandpaper with mineral composition presents additional manufacturing difficulties in a high-speed, speed, low-cost, GMP/QSR facility.
Minnesota Mining and Manufacturing Company has recently developed a technology that can produce a surface topography that microreplicates each element in the topography. Examples of the microreplication technology is disclosed in U.S. Pat. Nos. 5,672,097 and 5,658,184 and in copending, coassigned, U.S. patent application Ser. No. 08/514,417; now abandoned the disclosures of which are incorporated herein by reference.